The invention relates to an electrode binder composition, an electrode made using the described binder composition, and an electrochemical cell made using the described electrode, where the all of these materials are made using a composition of a poly(dialkylene ester) thermoplastic polyurethane composition. The electrode is made using the described thermoplastic polyurethane and an electrode active material. The electrochemical cells can be made using the described electrodes and also using (i) membranes and/or separators made using the described poly(dialkylene ester) thermoplastic polyurethane composition; (ii) an electrolyte system based on the described poly(dialkylene ester) thermoplastic polyurethane composition; or (iii) a combination thereof.
With the increasing supply of portable electronic devices, such as PDAs, mobile phones and laptop computers, their use range has been widened. Accordingly, the requirement for more compact, thinner, and lightweight batteries with high performance as power sources has been increasing, and much research on batteries has been conducted. Since lithium batteries are lightweight and have higher energy density, they have been used as major power sources for such portable devices. There is a need to improve the overall performance of electrochemical cells and so there is a need to improve the components that make up the electrochemical cells.
Cathode active materials for lithium batteries may include Li-containing transition metal oxides, such as LiCoO2, LiNiO2, LiMn2O4, LiFePO4, and chalcogen compounds, such as MoS2. Since these compounds have layer-crystalline structures, Li ions can be reversibly intercalated or deintercalated. Accordingly, these compounds have been widely utilized as cathode active materials for lithium batteries.
Metal lithium can be used as an anode active material. However, lithium ions of lithium are intercalated and deintercalated. Then, needle-shaped lithium dendrites grow on the surface of lithium because the lithium repeatedly dissolves and precipitates during charging/discharging of the battery. The needle-shaped dendrites have lower charge/discharge efficiency and can cause internal short-circuits by contacting a cathode. In addition, lithium metal can be very unstable in these applications due to its reactivity with oxygen and moisture.
To solve these problems, use of lithium alloy, metal powder, graphitic or carbonaceous materials, metal oxides, or metal sulfides, which can reversibly intercalates and deintercalates Li ions, as an anode material is under consideration. However, when a sheet-type anode made of a lithium alloy is used in a battery, the sheet-type alloy becomes thinner during charging/discharging, thereby degrading a current collecting property. Thus, the charge/discharge characteristics deteriorate.
When a sheet-type electrode is made of metal powder, a carbonaceous material, metal oxide, or metal sulfide powder, a binder is further used because these materials alone in powder form cannot form electrodes. For example, when manufacturing an anode using a carbonaceous material, it is common to add an elastic rubber-based polymer material as a binder.
When manufacturing an anode using metal oxides or metal sulfides, a conducting agent, in addition to the binder, is added to improve the charge/discharge characteristics. In general, when manufacturing an anode using a carbonaceous material, the carbonaceous material is pulverized into powder and a binder is added. However, if a conventional rubber-based polymer material is utilized as a binder, graphite particles may be coated depending on the amount of the binder, thereby hindering intercalation and deintercalation of lithium ions and deteriorating the high efficiency discharge characteristics.
If a conventional binder is used alone, regardless of the kind and form of a carbonaceous material, a large amount of binder should be added because a binding force between a metallic core material and the conventional binder is weak. However, when a large amount of binder is added to enhance the binding force, the surface of a carbonaceous material is coated by the binder. Therefore, the high efficiency discharge characteristics deteriorate. On the contrary, if a small amount of binder is used to maintain the discharge characteristics, the sheet-type electrode cannot be easily manufactured because a material for an electrode plate separates from the core material. Furthermore, the failure ratio increases in the manufacture of electrode plates.
Therefore, there is a need for binders that can be used in electrode such that the resulting electrodes perform at least as well as conventional electrodes and that address one or more of the problems described herein. In other words, there is a need for improved electrode binders, electrodes made from such binders, and electrochemical cells that use one or more such electrodes that address the problems seen in the current alternatives.